My 420 engages the engine fan full lock once the temp is at 85C....it keeps it engaged until its back down to about 81-82C.....it has never needed the electric fan so far...

My 300SD powers up the aux fan idling around 84C....and will stay on until I've been moving again for a while. With my old original radiator it'd get up to 105-110C working it on a hot day or idling in hot weather. With new radiator, t-stat, pump, and coolant, I've never seen it over 85 even on the hottest days.

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